1. Field of the Invention
The present invention relates to a circuit device, and more particularly to a signal transfer system in which semiconductor integrated circuits are mounted on a printed circuit board.
2. Description of the Related Art
When a synchronization circuit is mounted on a printed circuit board on which a lot of integrated circuits for memories and registers and so on are mounted, signals are outputted to the lot of integrated circuits. In this case, there is necessarily a case where signal receiving integrated circuits are located far apart from a signal outputting integrated circuit for the layout of the integrated circuits on the printed circuit board. Therefore, one integrate circuit can receive the signal without influence by reflection while one integrated circuit receives the signal influenced by reflection. For this reason, a buffer is generally provided in front of the input terminal of the integrated circuit in which the waveform of the received signal is distorted. Instead, a filter is provided or a design change is performed.
As mentioned above, when the lot of integrated circuits are mounted on the printed circuit board, one integrated circuit receives a signal distorted because of the influence of reflection. In this case, noise at an input terminal can not be avoided in spite of use of a single signal line, depending upon the mounted positions of the integrated circuit. The noise becomes a direct cause of an erroneous operation. If the amplitude of the noise exceeds an absolute maximum value, the integrated circuit is destroyed in many cases.
In accordance with, a design change would be accomplished or a buffer circuit would be inserted in front of the input terminal for the noise reduction as the result of system evaluation of the printed circuit board after the integrated circuits are mounted on the printed circuit board.
For this reason, the evaluation period became long and also the packaging density and power consumption are increased. Moreover, the design change is required to eliminate the waveform distortion dependent upon printed circuit board in the mass production of the printed circuit board.